Biomagnetometer with whole head coverage of a seated or reclined subject

ABSTRACT

A biomagnetometer includes a dewar vessel having a helmet-shaped recess at the lower end of its body. The recess is angled at about 45 degrees to the dewar body axis of the dewar vessel. Biomagnetic sensors are positioned within the interior of the dewar vessel body around the periphery of the recess. The angled recess permits the biomagnetometer to be used with subjects whose heads are inclined from 0 to 90 degrees to the horizontal by pivoting the dewar vessel over an angle of from -45 degrees to +45 degrees to the vertical, without spilling the cryogenic fluid within the dewar or causing excessive evaporation of the cryogenic fluid.

BACKGROUND OF THE INVENTION

This invention relates to the measurement of magnetic fields produced bythe brain of a human subject, and, more particularly, to an approach forperforming such measurements using an array of sensors surrounding thehead of the subject.

The human brain produces electrical signals. These electrical signalsare very faint, but they can be measured noninvasively by variousapproaches. One such technique, biomagnetometry, is based upon themeasurement of the magnetic fields produced outside the head of thesubject by the electrical current flows of the brain.

A biomagnetometer is a specially adapted, highly sensitive device havinga magnetic field sensor, a detector of electrical current flow in thesensor, and associated electronics. The magnetic field sensor istypically a single-loop or multiple-loop coil of wire which produces asmall current flow when a magnetic flux penetrates the loop. The sensoris desirably placed as closely as possible to the head of the subjectwhose brain signals are to be measured, because the strength of themagnetic field decreases rapidly with distance from the source. Thedetector is typically a superconducting quantum interference device("SQUID"), which can detect very small electrical currents.

The sensor and the detector are made of superconducting materials. Theyare operated at very low temperatures in order to attain theirsuperconducting states and also to suppress noise sources that increasewith increasing temperature. Currently available sensor/detectorelements are operated at liquid helium temperature, about 4.2° K. Inorder to be maintained at this temperature, the sensor and detector areplaced into an insulating vessel termed a dewar, and cooled with liquidhelium. A typical dewar is about 24 inches in diameter and 48 inches inlength. The size of the dewar and the need to place the sensors asclosely as possible to the head of the subject dictate careful geometricdesign of the dewar. In the usual practice, the sensors are placed intoa small-diameter extension of the main dewar vessel, termed a dewartail, that can be positioned closely to the head of the subject.

The preceding discussion has described a single measurement channelhaving a single sensor and its associated single detector. The earliestbiomagnetometers were built around a single measurement channel, butlater designs have incorporated multiple measurement channels into asingle unit. Current biomagnetometers have tens of measurement channels,and future instruments may have even more.

An important trend in the advance of biomagnetometry is the developmentof a capability for full-head coverage of subjects. That is, the sensorsmay be arranged in an array that is positioned around the head of thesubject. The magnetic fields produced by the brain of the subject aremeasured by all of the sensors simultaneously. The measurements areanalyzed to determine the position and strength of the source or sourceswithin the brain.

Various methods for positioning, cooling, and supporting the full-headarray of sensors have been proposed. In one, the lower end of the dewaris shaped in the manner of a helmet that fits over a portion of theentire head of the patient. The subject sits fully upright in a chair,and the dewar is lowered over the head of the subject until as close afit as possible is attained. The sensors are immersed in a liquid heliumreservoir inside the dewar and positioned about the inner surface of thehelmet-shaped recess. By this approach, the well-known technology ofexisting biomagnetometers is used with a specialized configuration ofthe lower end of the dewar in order to perform full-head measurements ofthe subject.

The present inventor has recognized that, while such an approach isoperable and useful, it also has shortcomings. Perhaps most importantly,the presently proposed biomagnetometers having full-head coverage areoperable only when the subject is sitting in a rigidly defined uprightposition. Many subjects cannot be presented in an upright position dueto their illnesses or infirmities. In one important application, thesubject may be a candidate for surgery that is to be performed with thepatient in a reclining position. The biomagnetic measurements are usedto aid the neurosurgeon in planning the surgery, which must be conductedvery precisely in order that vital areas of the brain not be damaged. Ameasurement performed on the sitting subject may not be applicable forcertain surgical procedures undertaken with the patient reclined becauseof a slight shifting of the location of the brain that is known to occurbetween the sitting and the reclining positions. Thus, it is highlydesirable to perform the biomagnetic measurements with the subject inthe reclining position for this particular application.

The dewar containing the sensors cannot be arbitrarily positioned at anydesired angle in order to fit the helmet-shaped recess over the head ofthe subject, because the dewar contains liquefied gas that can shift toexpose otherwise-submerged detectors or even spill if the dewar istilted at too steep an angle. A high tilt angle of the dewar can alsoexpose and effectively short thermal pathways, resulting in a highevaporation rate of the liquefied gas. One solution to the problem ofperforming full-head measurements is to supply two dewars, one forsitting and one reclining subjects. This approach is expensive and notfully satisfactory, because it may be desirable to position the subjectat an intermediate position between upright and reclining positions.Various types of dewars with movable lower ends can also be envisioned,but these designs are complex, are subject to leaks, are heavy, and arenot readily realizable with currently available materials.

There is a need for an improved approach to performing full-headbiomagnetic measurements of a subject. The present invention fulfillsthis need, and further provides related advantages.

SUMMARY OF THE INVENTION

The present invention provides a full-head coverage biomagnetometeroperable with the subject in a fully upright, fully reclined, orintermediate position. A single dewar having a fixed construction isused. Known techniques of dewar wall fabrication and other manufacturingprocedures are employed to minimize the chances of leakage and toutilize existing design-optimization practices.

In accordance with the invention, an apparatus for performingbiomagnetic measurements comprises a dewar vessel, an array ofbiomagnetic sensors within the dewar, and means for detecting signalsproduced by the biomagnetic sensors. The dewar vessel comprises aninsulated, liquid-tight, elongated hollow body having a dewar body axisparallel to a direction of elongation of the dewar body. The dewarvessel also includes a recess surface having a recess surface cranialportion substantially in the shape of a headform cranial portion of ahuman headform. The headform is defined by a generally cylindricalsurface having a headform reference axis coincident with the cylindricalaxis and is further defined by the headform cranial portion configuredto embrace the human cranium and having a headform cranial peripherycontinuous with the generally cylindrical surface. The recess surface isoriented such that the headform reference axis is at an angle to thedewar body axis of from about 30 degrees to about 60 degrees, mostpreferably about 45 degrees. The array of biomagnetic sensors ispositioned around at least a portion of the periphery of the recesssurface.

Alternatively, the recess may be described as an elongated recess in anexternal surface of the hollow body. The recess is sized sufficientlylarge to receive a human head therein such that the forehead, cranial,and occipital regions of the head are received therein. The recess has arecess axis parallel to the direction of elongation of the recess. Therecess axis is oriented at from about 30 to about 60 degrees to thedewar body axis.

The sensor array is preferably positioned closely adjacent to the innersurface of the recess, so that the sensor array is inclined at the sameangle as the recess. The recessed, helmet-like wall of the dewar body isplaced over the head of the subject to provide full-head sensorcoverage.

The recess and the sensor array are oriented at an angle of from about30 to about 60 degrees to the dewar body axis. The most preferredangular relation is 45 degrees. With this most preferred construction,the dewar vessel is pivoted about an axis in a horizontal plane at anangle of about -45 degrees to the vertical to accommodate a subjectsitting in the fully upright position. In this orientation, the recessand sensor array open downwardly and receive the head of the uprightsubject. To accommodate a fully reclining (horizontal) subject, thedewar is pivoted about the same axis to an angle of about +45 degrees tothe vertical. In this orientation, the recess and sensor array openhorizontally, and receive the head of the reclining subject. Tests haveshown that conventional dewars can be readily pivoted using a dewarsupport system between the -45 and +45 degree positions without damageto the dewar. An important virtue of the present design and approach isthat it also accommodates any intermediate position of the head of thesubject between the upright and reclining positions, by adjusting thepivoting position of the dewar. For some neurosurgery, for example, itmay be preferred that the patient be placed in such an intermediateposition for best access by the neurosurgeon.

The present invention provides an important advance in the art ofbiomagnetometry, and specifically full-head coverage for measurements ofactivity within the brain of the subject. It is noted that various typesof stand-alone helmet configurations for biomagnetic monitors have beenproposed. Such designs do not operate in conjunction with a conventionaldewar, but instead simply sit on the head of the user. However, at thepresent time most of these stand-alone helmet designs are not readilyimplemented for a variety of reasons, and in any event helmet designsmay never be able to achieve the very low sensor temperatures requiredto realize the greatest sensitivity. The present approach provides abiomagnetometer design that is implemented in conjunction with knowndewar cooling technology and that can achieve liquid helium temperaturesin the sensors and detectors of the system.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings, whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side sectional view of the apparatus of theinvention used with a subject in a fully upright sitting position, andincluding the electronics used in signal analysis;

FIG. 2 is a schematic side sectional view of the apparatus of theinvention used with a subject in a fully reclining position;

FIG. 3 is an elevational view of the apparatus of the invention usedwith a subject in a position intermediate between fully upright sittingand fully reclining, within a magnetically shielded room that is shownin schematic section;

FIG. 4 is an elevational view of the apparatus of the invention usedwith a subject in a fully reclining position, within a magneticallyshielded room that is shown in schematic section;

FIG. 5 is a block flow diagram for the method according to theinvention; and

FIG. 6 is a schematic diagram of a frame of reference for analyzing theapparatus of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is embodied in a biomagnetometer apparatus 20 forobtaining biomagnetic data from a head 22 of a human subject 24. Theapparatus 20 includes an array 26 of magnetic field sensors in the formof pickup coils 28 for measuring small magnetic fields. The pickup coils28 may be magnetometers or gradiometers, or of other configuration asmay be appropriate for a particular application. The geometry andorientation of the array 26 of magnetic field pickup coils will bediscussed subsequently.

The output signal of each magnetic field pickup coil 28 is detected by adetector, preferably a superconducting quantum interference device("SQUID"). There is typically one SQUID 30 for each pickup coil 28.These components, together with the associated electronics, form asingle channel. A typical apparatus 20 may have tens of channels.

Both the magnetic field pickup coil 28 and the SQUID 30 are maintainedat a cryogenic operating temperature within a vacuum-insulated dewarvessel 34 that has a vacuum-supporting wall and appropriate insulation.An outer wall 35 of the dewar vessel 34 functions as its external body36, which can be described as having a dewar body axis 38. In apreferred form, an upper portion of the body 36 is cylindrical with adiameter of about 24 inches and a length (in the cylindrical portion) ofabout 48 inches. The dewar body axis 38 is coincident with thecylindrical axis of the cylindrical portion of the dewar body 36 in thiscase. The dewar body 36 functions as an insulated vessel that contains acryogenic liquid 40. The required type of cryogenic liquid 40 isdetermined in part by the cooling requirements of the SQUID. In mostinstances, measurements of signals produced by the brain require a lowtemperature to suppress temperature-dependent noise, and liquid heliumis used as the cryogenic liquid. The present approach is also operablein conjunction with advanced dewar designs in which the pickup coilsand/or SQUIDs are supported in a vacuum rather than immersed in thecryogenic liquid.

The electronics arrangement of the apparatus 20 is illustratedschematically in FIG. 1. The magnetic signals from the brain are sensedby the magnetic field pickup coil 28, which produces a small electricalcurrent output signal when penetrated by magnetic flux. The outputsignal of the pickup coil 28 is detected by the detector, in this casethe SQUID 30. The SQUID 30 produces an electrical voltage proportionalto the magnetic flux detected by the pickup coil. The output signal ofthe SQUID 30 is processed in an ambient-temperature electronic signalprocessor 42, which typically includes balancing, gain, amplifying, andfiltering circuitry, and stored and analyzed in a computer 44 as afunction of time. Each sensor channel results in a record of itsresponse to the magnetic field produced by all of the sources within thesubject brain, as those sources act simultaneously on the pickup coil ofthe sensor channel. For simplicity, FIG. 1 depicts only a single sensorchannel including a pickup coil and a SQUID, but in practice there istypically a signal processor 42 for each of the SQUID 30/pickup coil 28sets.

The apparatus 20 and the subject 24 are preferably , but notnecessarily, enclosed within a magnetically shielded room 46, alsotermed an MSR, that shields the apparatus from external influences. TheMSR 46 is shown schematically in FIGS. 3 and 4. By screening off theexternal influences, the amount of signal processing and filteringrequired to obtain a meaningful indication of the biomagnetic field arereduced. The signal processor 42 and computer 44 are typically locatedoutside the MSR 46, so that they do not interfere with the sensing ofthe magnetic field of the subject.

The basic structure of some components of this system are known. Theconstruction of vacuum enclosures is disclosed in U.S. Pat. No.4,773,952. The construction and operation of magnetic field sensors,including pickup coils, SQUIDs, and ambient-temperature SQUIDelectronics are disclosed in U.S. Pat. Nos. 3,980,076; 4,079,730;4,386,361; and 4,403,189. A biomagnetometer is disclosed in U.S. Pat.No. 4,793,355. Magnetically shielded rooms are disclosed in U.S. Pat.Nos. 3,557,777 and 5,043,529. The disclosures of all of these patentsare incorporated herein by reference.

As shown in FIG. 1, the pickup coils 28 are arranged in thehelmet-shaped array 26 that is contained within the wall 35. In thepreferred embodiment, an upper portion 50 of the wall 35 is cylindrical.A lower portion 52 of the wall 35 is shaped to include a helmet-shapedrecess 54 that is sized to receive the head 22 of the subject 24therein. It is desirable that the pickup coils 28 be as close aspossible to the magnetic field source within the brain of the subject24. The helmet-shaped recess 54 in the wall 35 is thereforecooperatively structured with the array 26 of pickup coils 28, so thatthe individual pickup coils 28 are positioned closely adjacent to theinterior wall of the helmet-shaped recess 54.

The surface of the recess 54 is substantially in the shape of a headformcranial portion of a human headform. FIG. 6 depicts a set of referencerelations that are useful in defining the orientation of the recess. Therecess is shaped to conform to a portion of the human head, and is alsooriented so that the angle of the recess to the dewar body axis 38 isfrom about 30 to about 60 degrees. The human head is not of a shape thatis easily defined by a single standard form. Various techniques havebeen employed to define the headform in a general sense. In one suchtechnique, the headform is defined as a cylinder that approximatelyconforms to the lower part of the head, topped by a curved headformcranial portion. This technique has been utilized, for example, by theInternational Standards Organization (ISO) in setting standards fortesting of protective helmets, see ISO Recommendation R1511 and DraftInternational Standard ISO/DIS 6220. See also U.S. Pat. No. 5,309,095.The disclosures of these publications are incorporated by reference.

These approaches both utilize a cylindrical headform portion thatdefines a headform axis (e.g., axis Z in FIG. 4 of the '095 patent). Theapproaches differ in that the headform cranial portion is definedempirically in the ISO publications and by a set of intersectinghemispheres and cones in the '095 patent.

For the purposes of the present invention, it is necessary to establishthe reference axis for the headform. Referring to FIG. 6, the headform90 is defined by a generally cylindrical surface 92 and a curvedheadform cranial portion 94 that is continuous with the cylindricalsurface 92. As used herein, the term "generally cylindrical" refers to asurface formed by moving a planar curve along an axis, termed the"cylindrical axis", that lies perpendicular to the plane in which thecurve lies. The generally cylindrical surface therefore has thecharacteristics of a right-circular cylinder, except that the crosssection is the planar curve, not a circle.

Preferably, a headform cranial portion periphery 96 is tangent to thegenerally cylindrical surface 92. The generally cylindrical surface 92has a cylindrical axis 98. A headform reference axis 100 is coincidentwith the cylindrical axis 98. The generally cylindrical surface 92 has asize such that the headform is inscribed therein. The shape of theheadform cranial portion is such as to embrace the human cranium,including the forehead, cranial region, and occipital regions. Forstandardization purposes, it is described either empirically (as in theISO standards) or by a set of approximate geometrical figures (as in the'095 patent). Either standardized approach, or any other operableapproach, may be used to define the shape of the headform cranialportion 94.

The recess 54 is shaped to conform to at least a portion of the headform90, and in particular to the headform cranial portion 94. The recess 54is oriented such that the headform reference axis intersects the dewarbody axis 38 at an angle of from about 30 to about 60 degrees, mostpreferably at an angle of 45 degrees. If the angle between the headformreference axis 100 and the dewar body axis 38 is less than about 30degrees or more than about 60 degrees, the dewar cannot accommodate therange of movement of the positions of the head of the subject withoutrequiring excessively large tilting of the dewar vessel 34. Suchexcessively large tilting may cause the cryogenic liquid in the vesselto spill or may expose the cooled elements within the vessel to resultin greatly reduced thermal efficiency.

From an apex 56 of the recess 54 and the headform 90, through which theheadform reference axis 100 passes, the wall of the recess 54 extendsboth outwardly (relative to the interior of the vessel 34) and to theleft in the view of FIG. 1, and outwardly and to the right. Thepreferred structure for the recess is to cover the forehead of thesubject on one side, and to cover the lower part of the head (occipitalregion) extending to the upper vertebrae of the spine on the other side.To state the distances involved in a preferred embodiment, it isobserved that the dewar body axis 38 and the headform reference axis 100define a pivoting plane. The section of FIG. 1 is made in that pivotingplane. The wall of the recess 54 includes a concavely curved (relativeto the interior of the vessel 34) recess wall first segment 60 thatextends outwardly from the inwardly extending point by a distance offrom about 21/2 to about 31/2 inches as measured parallel to theheadform reference axis 100, and to the left (as viewed in FIG. 1) adistance of from about 4 to about 41/2 inches as measured in thepivoting plane and perpendicular to the headform reference axis 100. Thewall of the recess 54 includes a concavely curved recess wall secondsegment 62 that extends outwardly from the inwardly extending point by adistance of from about 7 to about 8 inches as measured parallel to theheadform reference axis 100, and to the right (as viewed in FIG. 1) adistance of from about 4 to about 41/2 inches as measured in thepivoting plane and perpendicular to the headform reference axis 100. Therecess of these dimensions, and a width of about 7 inches (measuredperpendicular to the pivoting plane) provides full-head coverage formost persons. Other magnetic field pickup coils and their associateddetectors are positioned on the sides of the helmet-shaped recess, outof the plane of view of FIG. 1.

This angled arrangement of the recess 54 permits the apparatus 20 to beused without structural modification for the subject 24 in both theupright seated position shown in FIG. 1 and the fully reclined positionshown in FIG. 2. To accomplish this multipositional use, the dewarvessel 34 is rotated in the pivoting plane (defined by the intersectingdewar body axis 38 and headform reference axis 100). At a positionwherein the dewar body axis 38 is rotated -45 degrees from vertical, asshown in FIG. 1, the recess 54 opens vertically downwardly toaccommodate the subject 24 sitting fully upright. At a position whereinthe dewar body axis is rotated +45 degrees from vertical, as shown inFIG. 2, the recess 54 opens horizontally (to the left in FIG. 2) toaccommodate the subject 24 in a fully reclined position. The rotationsof -45 degrees and +45 degrees do not cause spillage of the cryogenicliquid 40, exposure of the SQUIDs 30 above the surface of the cryogenicliquid, excessively reduced thermal efficiency, or any other damage.

As shown in FIG. 3, the dewar vessel 34 is pivotably supported in asupport stand 64 that permits the dewar vessel 34 to be pivoted from the-45 degree position to the +45 degree position in the pivoting plane.The subject 24 rests on a subject support 66 that is illustrated as asegmented pad whose upper end can be pivoted upwardly. The subjectsupport 66 is raised or lowered by any operable approach, hereillustrated as a pneumatic bed 68.

A particular advantage of the approach of the invention is that itaccommodates the subject when sitting fully upright or fully reclining,and also any intermediate position. The fully upright position is notcomfortable for some persons, so a nearly fully upright, but slightlyreclined position such as illustrated in FIG. 3 can be used. The recess54 of the dewar vessel 34 is readily positioned to receive the head ofthe subject simply by changing the pivot angle from -45 degrees to alesser angle that is reduced from -45 degrees by the amount of the angleof the reclining of the head from the vertical.

To use the apparatus 20 with the subject in the reclining position (FIG.4) after it has been used in the sitting position (FIGS. 1 or 3), thesupport stand 64 and its dewar vessel 34 are moved away. The subjectsupport 66 is dropped to the horizontal position, and the pneumatic bed68 is raised. The dewar vessel 34 is pivoted to the +45 degree position.The support stand 64 is then moved into place with the helmet-shapedrecess 54 over the head of the subject, as shown in FIG. 4. (Themeasurement with the subject in the sitting position, FIGS. 1 or 3, isordinarily accomplished with the pneumatic bed 68 as low as possible inorder to provide overhead clearance for the dewar vessel 34 inside theceiling of the MSR 46.)

FIG. 5 depicts a method for performing biomagnetic measurements. Theapparatus 20 as described above is furnished, numeral 80. The subject ispositioned, numeral 82. The dewar vessel is positioned to permit thehead of the subject to be received within the helmet-shaped recess, andthe head of the subject is so placed, numeral 84. Biomagneticmeasurements are taken, numeral 86, typically using data from the entirearray of pickup coils extending around the head of the subject. Thesteps 82, 84, and 86 can be repeated as necessary with the subject inother positions, as described above in relation to FIGS. 3 and 4.

The present invention provides an advance in the utilization of thepotential of full-head coverage biomagnetic measurements. A singleapparatus can be used to accomplish full-head measurements withouthardware reconfiguration other than a simple tilting of the dewarvessel. Although a particular embodiment of the invention has beendescribed in detail for purposes of illustration, various modificationsand enhancements may be made without departing from the spirit and scopeof the invention. Accordingly, the invention is not to be limited exceptas by the appended claims.

What is claimed is:
 1. Apparatus for performing biomagneticmeasurements, comprising:a dewar vessel comprisingan insulated,liquid-tight, elongated hollow body having a dewar body axis parallel toa direction of elongation of the body, and an elongated recess having arecess axis parallel to a direction of elongation of the recess and arecess surface cranial portion substantially in the shape of a headformcranial portion of a human headform, the headform being defined by acylindrical surface having a headform reference axis coincident with thecylindrical axis and further defined by the headform cranial portionconfigured to embrace the human cranium and having a headform cranialperiphery continuous with the cylindrical surface, the recess axis beingcoincident with the headform reference axis and at an angle to the dewarbody axis of from about 30 degrees to about 60 degrees; an array ofbiomagnetic sensors within the dewar body and positioned around at leasta portion of the periphery of the recess surface; and means fordetecting signals produced by the biomagnetic sensors.
 2. The apparatusof claim 1, wherein the recess axis is oriented at an angle of 45degrees to the dewar body axis.
 3. The apparatus of claim 1, wherein thehollow body is substantially cylindrical in shape.
 4. The apparatus ofclaim 1, wherein the array of sensors includes a plurality of magneticfield pickup coils and the means for detecting includes a plurality ofsuperconducting quantum interference devices, each pickup coil having asuperconducting quantum interference device in electrical communicationtherewith.
 5. The apparatus of claim 1, further includingmeans forsupporting the dewar vessel and for pivoting the dewar vessel about ahorizontal axis through an angle of from about -45 degrees relative to avertical axis to about +45 degrees relative to the vertical axis.
 6. Theapparatus of claim 5, further includingmeans for supporting a head of apatient at an angle to a horizontal plane of from zero to 90 degrees. 7.The apparatus of claim 1, further includingmeans for supporting a headof a patient some angle to a horizontal plane of from zero to 90degrees.
 8. Apparatus for performing biomagnetic measurements,comprising:a dewar vessel comprisingan insulated, liquid-tight,elongated hollow body, the elongated hollow body having a dewar bodyaxis parallel to the direction of elongation of the body, and anelongated recess in an external surface of the hollow body, the recessbeing sized sufficiently large to receive a human head therein such thatthe forehead, cranial, and occipital regions of the head are receivedtherein, the recess having a recess axis parallel to the direction ofelongation of the recess, the recess axis being oriented at an angle offrom about 30 to about 60 degrees to the dewar body axis; and an arrayof biomagnetic sensors within the dewar body and positioned around atleast a portion of the periphery of an internal surface of the recess;and means for detecting signals produced by the biomagnetic sensors. 9.The apparatus of claim 8, wherein the recess axis is oriented at anangle of about 45 degrees to the dewar body axis.
 10. The apparatus ofclaim 8, wherein the hollow body is substantially cylindrical in shape.11. The apparatus of claim 8, wherein the array of sensors includes aplurality of magnetic field pickup coils and the means for detectingincludes a plurality of superconducting quantum interference devices,each pickup coil having a superconducting quantum interference device inelectrical communication therewith.
 12. The apparatus of claim 8,further includingmeans for supporting the dewar vessel and for pivotingthe dewar vessel about a horizontal axis through an angle of from about-45 degrees relative to a vertical axis to about +45 degrees relative tothe vertical axis.
 13. The apparatus of claim 12, further includingmeansfor supporting a head of a patient at an angle to a horizontal plane offrom zero to 90 degrees.
 14. The apparatus of claim 8, furtherincludingmeans for supporting a head of a patient at some angle to ahorizontal plane of from zero to 90 degrees.